There are (as of yet) no definitive data concerning the appropriate dose or the most tolerable delivery system for aerosolized pentamidine in pediatric patients with HIV infection who require prophylaxis against Pneumocystis carinii. Using a delivery and dosage regimen similar to that recommended for adult patients, we are assessing the tolerance of aerosolized pentamidine in children. All patients are receiving aerosolized pentamidine as prophylaxis based on a clinical indication of either sulfa intolerance or low CD4 counts. Specifically addressed in the assessment of tolerance are physiologic parameters, such as heart rate, respiratory rate, oxygen saturation, cough, and evidence of bronchospasm. Subjective assessment includes whether or not there was a bad taste or burning associated with the aerosolization of pentamidine. Tolerance data are being collected serially and chronologically on all HIV-infected children receiving this prophylaxis regimen in the MICU. To date, the major side effects have been bronchospasm that is reversible with bronchodilator aerosolization (5 of 22 patients) and coughing without oxygen desaturation (16 of 22 patients). Thus, preliminary data indicate good tolerance without serious side effects. This clinical project is ongoing.